These days, importance of global environmental has increased, so a wind power attracts scientists' attention as clean energy, and many types of wind mills have been studied and developed. A drag-based vertical shaft wind mill is capable of operating without wind direction control, and aerodynamic noise, bad influence to scenery and moving shadows are less than those of a horizontal shaft wind mill, e.g., a propeller type wind mill, so the vertical shaft wind mills are good to install on roofs of houses and buildings as small-scale electric generators. Torque of the drag-based vertical shaft wind mills are large, but rotational speeds and energy converting efficiency thereof are low, so the vertical shaft wind mills are not practically used, other than Savonius type wind mills, as electric generators.
To utilize the merits of the drag-based vertical shaft wind mills and use the wind mills as small-scale electric power plants, an output power must be increased, so the conventional Savonius type wind mills have been improved.
For example, a Savonius type wind mill having fixed vanes, which are provided on the outer side of rotary blades so as to introduce a large amount of air to the rotary blades and reduce resistance caused by wind, is disclosed in Japanese Patent Gazette No. 11-62813.
Another Savonius type wind mill having at least one rotatable reflector, which is provided on the outer side of rotary blades so as to adjust air flows, improve an output power and make the output power stable, is disclosed in Japanese Patent Gazette No. 2001-289150.
However, in the Savonius type wind mill disclosed in Japanese Patent Gazette No. 11-62813 which has the fixed vanes provided on the outer side of the rotary blades, a part of air flows introduced by the fixed vanes collide with rear faces of the rotary blades (faces on the forward sides of the rotary blades), so that the rotation of the wind mill is hindered. On the other hand, in the Savonius type wind mill disclosed in Japanese Patent Gazette No. 2001-289150 which has the reflector separated away from the rotary blades, a size of the wind mill must be large in comparison with a diameter of a rotor.
In the Savonius type wind mill, if overlapped parts of rotary blades, each of which are formed into a half cylindrical shape, are small, tip speed ratio is decreased by increasing load so that air flows stay on the front side of the rotary blades (on wind receiving face sides of the rotary blades) and a braking force works to the rotary blades on an upper stream side. If the overlapped parts are made large so as to avoid this disadvantage, the rotary blades must be large in comparison with a rotor so that the rotary blades must be heavy.
Namely, in the Savonius type wind mills, it is impossible to efficiently convert air flows, which have been intercepted, collected and straightened by the fixed vanes, into torque, so that it is difficult to highly increase the output power. For example, in the Savonius type wind mill disclosed in Japanese Patent Gazette No. 2001-289150, two reflectors, whose sizes are ½ of the diameter of the rotor, are provided on the upper stream side, maximum increase of the output power is about 50% even if positions and angles of the reflectors are adjusted, therefore substantial increase of the output power is not so large in spite of providing the reflectors which makes the wind mill larger.
In the gazette, the drag-based vertical shaft wind mill is capable of electrically controlling the positions and the angles of the reflectors, which are provided on the outer side of the Savonius rotor, so as to automatically control the rotational speed of the rotor and automatically protect the rotor against strong wind, but a complex structure including a mechanism for moving the reflectors, an electric power source, a motor, a wind direction sensor, a control unit, etc. is required.
Thus, the present invention was invented to solve the disadvantages of the conventional wind mills, and an object of the present invention is to provide a vertical shaft driving device, which is capable of generating a high output power in comparison with the conventional vertical shaft Savonius type wind mills (especially under high load) and controlling rotation of the device so as to automatically protect against strong wind without an external driving source, and an electric generator driven by the driving device.
Note that, water wheels driven by water flows have been used as devices employing natural energy. Water wheels are also required to efficiently use water flows, so water wheels driven by ocean streams, tides, etc. have the same disadvantages as the wind mills have.
In the present specification, the word “vertical shaft driving device” means an device for rotating a vertical shaft by natural energy, e.g., air flows, water flows.